Recent data from the St. Louis Carotid Occlusion Study have demonstrated that Stage II hemodynamic failure [ipsilateral increased oxygen extraction fraction (OEF) measured by positron emission tomography] is a powerful independent risk factor for subsequent stroke in patients with symptomatic carotid occlusion. After adjustment for 17 baseline patient characteristics and interval medical treatment, the relative risk conferred by Stage II hemodynamic failure was 7.3 (95 percent CI 1.6 - 33.4) for ipsilateral ischemic stroke corresponding to two year rates for ipsilateral stroke of 5.3 percent in 42 patients with normal OEF and 26.5 percent in 39 patients with increased OEF (p=.004). Previous studies have demonstrated that surgical anastomosis of the superficial temporal artery to the middle cerebral artery (STA-MCA) can restore these hemodynamic abnormalities to normal. This current proposal is for a planning grant to complete the remaining steps necessary to develop a detailed study protocol and to organize the research group for a full scale clinical trial. The specific aims for the proposed full scale clinical trial are to test the hypothesis that STA-MCA surgical anastomosis when added to best medical therapy can reduce by 33 percent, despite perioperative stroke and death, subsequent ipsilateral ischemic stroke (fatal and non-fatal) at two years in patients with recently (less than or equal to 120 days) symptomatic internal carotid artery occlusion and Stage II hemodynamic failure. We will conduct a randomized non-blinded controlled trial in a maximum of 664 patients. We will employ an innovative two-stage design to first carry out a pilot phase of 200 patients which will permit us to gather information regarding surgical morbidity and mortality, confirm the two-year stroke rate in the non-surgical group and provide data on recruitment. Following the pilot phase, the NINDS PSMB will make a decision to (1) halt the trial because demonstrated difference between the two groups meets the early stopping rule (p less than .005) (2) continue the trial to completion given the newly calculated sample size based only on the two year ipsilateral stroke rate in the non-surgical group, (3) halt the trail because the recruitment rate indicates that the necessary sample size is not realistic or (4) halt the trial because it is almost certain not to show a benefit of surgery. We will use the period of the planning grant to: (1) Recruit and certify centers, (2) Establish enrollment timetable, (3) Complete protocol and manual of operations, (4) Generate data forms, (5) Establish committees, (6) Prepare training schedule and materials, and (7) Prepare budgets.